SMTA International Conference Proceedings

Device Assembly Considerations for Integration of One-Step Chip Attach Materials in Conventional Reflow Processing

Authors: Joseph Biggs, Hemal Bhavsar, Bruno Tolla, Ph.D.
Company: Kester, An ITW Company
Date Published: 9/17/2017   Conference: SMTA International

Abstract: One step chip attach materials (OSCA) are polymeric materials for flip chip assembly, which are designed to flux metallic interconnections and turn into an underfill upon curing. Prior work has demonstrated the theoretical potential for an OSCA material to simplify the flip chip assembly process by removing the need to have distinct fluxing, reflow, defluxing and underfilling stages in the assembly line: OSCA materials can allow these processing steps to be consolidated. OSCA materials designed for conventional mass reflow processing are designated “OSCA-R.” The critical challenges in designing OSCA-R materials have been heavily detailed in earlier studies [1]. Once a suitable OSCA-R candidate material has been derived, we have identified several critical factors that exist in the assembly process which must be understood to successfully integrate a candidate OSCA-R material with a typical flip-chip assembly process using conventional reflow methods. This paper addresses the observed effects of dispensing parameters, placement conditions, and carrier effect during reflow on device pass rates using a typical MEMS package as a test vehicle.

While the consideration of filler particles has been shown to be a critical factor in OSCA-R performance, other assembly parameters like device placement, dispensing conditions, and the effect(s) of the carrier system used for the substrate during reflow may not be studied in detail during material design phases. However, we demonstrate that the consideration of these assembly parameters is critical for establishing a successful integration of mature OSCA-R technologies with existing conventional reflow processes. This paper presents research focused on understanding the impact of dispensing conditions on accuracies and variability in OSCA-R transfer on the substrate, which in turn directly impacts die attach performance; additionally, the effect of placement force and speed is investigated on semiconductor packages; finally, the carrier system effect on soldering performance after conventional reflow processing is quantified and mitigated through process optimization. Preliminary results indicate that the robust integration of OSCA-R technologies into existing reflow processing schemes requires a multimodal approach combining material design considerations with dedicated application work focused on establishing a robust device assembly process. This can be best realized through a partnership leveraging the material supplier expertise and the end-user industrial manufacturing knowledge.

Key Words: 

One-Step Chip Attach (OSCA); Reflow; Semiconductor Packaging

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